A conventional microscopic spectrometer is shown in FIG. 4. Therein, light from a light source 1 is incident upon a sample 2. The light transmitted through sample 2 is focused by an object lens 3 to form an enlarged image on an image surface 4. The image surface 4 is enlarged and focused into a second image through a relay lens 5, which allows the image surface 4 to be observed by an eyepiece 6.
When the spectrometric measurement is conducted, the light is introduced into the spectrometrical measurement system 8 by placing a mirror 7 between the image surface 4 and the relay lens 5. The mirror 7 changes the optical path so that the light travels through the spectrometrical measurement system 8, thereby allowing a spectrometric analysis and the production of a display 9.
An example of an object to be spectrometrically measured is illustrated in FIG. 5. The sample 2 may include several areas A, B, and C. Oftentimes the user does not wish to spectrometrically measure the entire sample 2, but prefers to merely measure the area A alone.
The spectrometrical measurement is made by masking the image surface 4. This masking operation is shown in FIG. 5. The image surface 4 is provided with masks 10 and 11 which are disposed one on top of the other. The masks 10 and 11 are opaque and provide an optical throughput only where neither mask 10 nor mask 11 have a portion. Masks 10 or 11 used in combination mask out all portions of the sample 2 which are not meant to be measured.
As shown in FIG. 6, masks 10 and 11 are movable along axes which are respectively perpendicular. Thereby, any area A within the sample may be selected, and the rest of the sample 2 is masked. The masks 10, 11 provide an optical throughput and thereby allows a measurement to be conducted.
Because the conventional microscopic spectrometer depicted in FIGS. 4-7 mask all areas of the sample 2 other than the area A to be measured, it is impossible to reconfirm a positional relation of the area A with respect to the entire image of the sample 2 through simple visual observation. Since the physical masks 10, 11 block out sample 2 except for the area A, the positional relationship of the area A is lost. This difficulty becomes further exaggerated as the object to be measured becomes more minute or complicated, i.e., in a semiconductor chip or cellular tissue.
In order to reconfirm the positional relationship of an area A which is being measured, the masks 10, 11 must be removed or the slit allowing optical throughput must be moved. Once the mask is removed or the slit is moved, it is extremely difficult to reproduce the exact position of the masks 10, 11, and thereby reproduce the exact measurement that is being taken. Thus, the accuracy of the spectrometrical measurement is greatly decreased.